2014 AAOS Annual Meeting

10/10/2014

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2014 AAOS Annual Meeting

Presentation Abstract Session:

211-225-Spine II

Date/Time:

Tuesday, Mar 24, 2015, 4:30 PM - 4:36 PM

Location

Venetian/Sands EXPO, Room 3105

Presentation Number:

Paper 215

Title:

Global Sagittal Angle (GSA): A Novel Parameter To Address Sagittal Alignment And Compensatory Mechanisms In The Body

Classification: +Diagnostics/imaging (Spine) Keywords:

Scoliosis / Deformities; Spondylolisthesis / Spondylolysis; Cervical

Author(s):

Bassel G. Diebo, MD Shian Liu Renaud Lafage Vincent Challier, MD Emmanuelle Ferrero Themistocles S. Protopsaltis, MD Thomas J. Errico, MD Frank J. Schwab, MD Virginie Lafage, PhD

Abstract:

Introduction:In the setting of spinal pathologies, the musculoskeletal system provides a wide range of compensatory mechanisms to maintain the sagittal alignment and horizontal gaze. Many parameters correlated with Health Related Quality of Life (HRQOL) have been proposed to quantify either the deformity or the compensatory mechanisms. However, to date, no parameter has been able to account for spine deformity and lower limbs compensatory mechanisms involved in the sagittal plane, while correlating with quality of life and disability scores. We propose a novel, clinically relevant angle which accounts for spinal deformity, as well as spino-pelvic and lower extremity compensatory mechanisms: the global sagittal angle (GSA), defined as the angle subtended by a line from the midpoint between the femoral condyles to the center of C7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S1 sacral endplate (Figure 1).

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Methods:This is a retrospective review of patients who underwent full body stereoradiography between 2012 and 2013 for spinal pathologies. The primary diagnoses were scoliosis, low back pain, degenerative spondylolisthesis, spinal stenosis and degenerative disc disease. Oswestry disability index (ODI) was collected. Radiographic measurements were performed using a validated spine dedicated software to quantify the following cervical, lumbar, pelvic and lower extremity parameters: Chin Brow Vertical Angle (CBVA), C2-C7 cervical lordosis (CL), C2-C7 sagittal vertical axis (cSVA), slope of the MacGregor line (McGSS), Slope of the Line of Sight (SLS), lumbar lordosis (LL), pelvic incidence (PI), pelvic retroversion (PT), Knee flexion angle (KA), Ankle flexion angle (AA), and Pelvic shift (P.Sh), Sagittal Vertical Axis (SVA) and T1 pelvic angle (TPA). Global Sagittal angle, GSA (the angle of the line between middle of C7 vertebra to the knee, to the midpoint between the two femoral condyles and the line between this point and posterior superior corner of S1), was proposed. Results:80 patients met inclusion criteria and had a mean age of 51.64+18.6yrs, BMI 27.5, with 76.3% females. Diagnoses were: 40 scoliosis, 13 low back pain, 13 degenerative spondylolisthesis, 10 spinal stenosis, and 4 degenerative disc disease. Mean GSA angle for the overall cohort was 4.73°±5.97°. For patients with severe sagittal malalignment as defined by the SRS-Schwab classification (PI-LL, PT, and SVA graded as ++), the mean GSA was 20.39°±0.12°. GSA angle was the most correlated with HRQOL (ODI) (r = 0.408, p = 0.001). GSA was significantly correlated with all radiographic parameters (p < 0.05) especially: CBVA (r = -0.324), CL (r = -0.446), PI-LL (r = 0.761), PT (r = 0.483), KA (r = 0.775) (Figure 1). A subset of patients had minimal to no spinal malalignment or compensatory mechanisms, and had a mean GSA of -1.30°+1.35° (ie knee, S1, and C7 were on the same vertical line) Discussion and Conclusion:GSA is a simple, novel angle to assess the sagittal plane of the human body. GSA is highly correlated with spinal alignment parameters, and pelvic and lower extremities compensatory mechanisms related to spinal pathologies. GSA is also strongly correlated with ODI, even more so than SVA, suggesting its clinical relevance.

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